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Title: High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior

Abstract

We report high resolution 15N NMR probing of the solid-solid phase transition of 15N-labeled ammonia borane (NH3BH3) around 225 K. Both the 15N isotropic chemical shift, δiso, and the spin-lattice relaxation rate (T1-1) exhibited strong anomalies around 225 K. The analysis of T1-1 using the Bloembergen-Purcell and Pound model showed that the motional correlation time, τ, increased from about 1 ps to 100 ps while the corresponding Arrhenius activation energy increased from 6 to 13.4 kJ/mol on going through the transition. The observed strong temperature dependence of δiso was interpreted by an extension of the Bayer model. The time scale of the underlying motion was found to be in a reasonable agreement with the T1-1 data. These results imply that the NH3 rotor motion plays a pivotal role in the transition mechanism, and that the transition is of both order-disorder and displacive type. This work was supported by the Office of Basic Energy Sciences of the U. S. Department of Energy Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for the U. S. Department of Energy.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
901463
Report Number(s):
PNNL-SA-52116
KC0302010; TRN: US200714%%22
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry B, 111(4):677-681; Journal Volume: 111; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AMMONIUM COMPOUNDS; BORANES; ACTIVATION ENERGY; CHEMICAL SHIFT; RESOLUTION; SPIN-LATTICE RELAXATION; NUCLEAR MAGNETIC RESONANCE; PHASE TRANSFORMATIONS; 15N NMR; ammonia borane; phase transition

Citation Formats

Gunaydin-Sen, Ozge, Achey, Randall, Dalal, Nar S., Stowe, Ashley C., and Autrey, Thomas. High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior. United States: N. p., 2007. Web. doi:10.1021/jp0649347.
Gunaydin-Sen, Ozge, Achey, Randall, Dalal, Nar S., Stowe, Ashley C., & Autrey, Thomas. High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior. United States. doi:10.1021/jp0649347.
Gunaydin-Sen, Ozge, Achey, Randall, Dalal, Nar S., Stowe, Ashley C., and Autrey, Thomas. Thu . "High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior". United States. doi:10.1021/jp0649347.
@article{osti_901463,
title = {High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior},
author = {Gunaydin-Sen, Ozge and Achey, Randall and Dalal, Nar S. and Stowe, Ashley C. and Autrey, Thomas},
abstractNote = {We report high resolution 15N NMR probing of the solid-solid phase transition of 15N-labeled ammonia borane (NH3BH3) around 225 K. Both the 15N isotropic chemical shift, δiso, and the spin-lattice relaxation rate (T1-1) exhibited strong anomalies around 225 K. The analysis of T1-1 using the Bloembergen-Purcell and Pound model showed that the motional correlation time, τ, increased from about 1 ps to 100 ps while the corresponding Arrhenius activation energy increased from 6 to 13.4 kJ/mol on going through the transition. The observed strong temperature dependence of δiso was interpreted by an extension of the Bayer model. The time scale of the underlying motion was found to be in a reasonable agreement with the T1-1 data. These results imply that the NH3 rotor motion plays a pivotal role in the transition mechanism, and that the transition is of both order-disorder and displacive type. This work was supported by the Office of Basic Energy Sciences of the U. S. Department of Energy Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for the U. S. Department of Energy.},
doi = {10.1021/jp0649347},
journal = {Journal of Physical Chemistry B, 111(4):677-681},
number = 4,
volume = 111,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}